Electronic musical instrument



May 6, 194-1.

R. W. BUMSTEAD ELECTRONIC MUSICAL INSTRUMENT 4 Sheets-Sheet 1 Filed Nov.30, 1939 T0 SIMILAR TUNING FOR/(5)7 AND KEYS 37FOREACl-l NOTE IN THEMUSICAL SCALE /9 I I I /7 I M M- I CLARINET TONE ORGAN TONE INVENTORRALPH W. BUMSTEAD 7 ,aru-vl/ ATTORNEY M y 1941- v R. w; BUMSTEAD2,241,627

ELECTRONIC MUSICAL INSTRUMENT Filed Nov. 50, 1939 4 Sheets-Sheet 2 9 o Dog l W O- //Z5 FLUTE 0 6'6 5,

me 3 I 9 6 4MP! IFIER LOUDSPfA/(ER INVENTOR RALPH W. BUMSTEAD ATTORNEYMay 6, 1941. R. w. B UMSTEAD ELECTRONIC MUSICAL INSTRUMENT Filed NOV.30, 1939 4 Sheets-Sheet 5 WIDTH 0F ZONE SCAA/A/ 5r CATH- 005 s ar 0TH orz0,v

NNED ar CA Tl-IODf pm "spar" I INVENTOR RALPH W. B MSTEAD BY ATTORNEYD/A PA SON May 6, 1941.

R. w. BUMSTEAD ELECTRONIC MUSICAL INSTRUMENT Filed Nov. 30, 1939 4Sheets-Sheet 4 I NV EN TOR.

RALPH w BUMSTEAD ATTORNEY.

Patented May 6, 1941 a 2,241,027 annc'rnomc MUSICAL ms'rnmmnr Ralph W.cad, Westfield, N. L, asslgnor to Radio Corporation of America, acorporation of Delaware Application November 30, 1939, Serial No.306,942

k 19 Claims.

This invention relates to electronic musical instruments and moreparticularly to a device for controlling the modulation of electricwaves in accordance with the playing of keys on one or more keyboards,such as are comprised in a console of an organ. The methods employed aresuch as to superimpose selected harmonics or overtones upon thefundamental frequencies which are appropriate to the different keys ofthe keyboard.

The instant application is a continuation-inpart of my co-pendingapplication Serial No. 86,740, which was filed June 23, 1936.

My invention has particular utility in musical instruments, such, forexample, as an electronic comparison with other notes whichare'simultaneously played as an accompaniment.

,It is another object of my invention to provide an electronic musicalinstrument which comprises an iconoscope tube of the general typeheretofore used in television systems, this tube being operative tomodulate the fundamental frequency tones of the keys which are played,so as to give these tones a desired timbre characteristic.

It is a still further object of my invention to provide electronicapparatus such as will'properly correlate the harmonic content of toneswith their fundamental frequencies. In making this correlation itappears to be desirable that the phase relationships existing betweendifferent overtones or harmonics of a given fundamental frequency shallbe consistently maintained and not tones together with a number of theharmonics thereof and to amplify the resultant of the waves so combined,and to impress the output energy from an amplifier on any convenientsound reproducing device.

periodically reversed, as would be the case when utilizing certain ofthe devices heretofore employed. Thus, instead of scanning a character-'istic wave pattern back and forth in order to One of the difficultiesencountered in the syn- The difiiculty is that musical tones to which wehave accustomed our ears are of a very complex nature. Often times thetone of an organ pipe or an orchestral instrument includes as many asthirty significant harmonics of a given fundamental tone. Thecombination of so many harmonics with the fundamental in their correctproportions by prior knownmethods involves the use of very cumbersomeapparatus and intricate circuits. Furthermore, the controls which wouldi need to be provided in place of "organ stops would be multitudinousand difllcult for a musician to manipulate.

Accordingly, it is among the objects of my invention to provide amultiple harmonic generator in which one element only is necessary forcompounding the required harmonics of every tone in the musical scale inorder to give the tone. quality of the fundamental notes a given timbrecharacteristic. The duplication of such elements in order to provide arange of tone qualities in the output of an electric organ would:therefore, correspond with the number of stops which it may be desiredto provide.

It is another object of my invention to provide electrical apparatus incombination with the manual and pedal keyboards of an organ console,such as will enable anorganist to play a musical selection using thedifferent manuals and pedal keyboard in the usual manner for emphasizingcertain notes, which represent a solo passage in 60 modulate afundamental frequency by superimposed odd harmonics, the phase of whichwould be reversed with each half cycle of the fundamental frequency, Ipreferably provide scanning means which is rotational in character sothat these phase relationships maybe properly maintained.

In carrying out my invention I propose to use for the synthesis ofharmonics, such as to produce tones of a given quality or timbre, acathode ray tube having the usual cathode, focussing anode anddeflecting plates and a novel form of anodes against which the cathoderay beam may be projected. Such a cathode ray tube is not of the typehaving a fluorescent screen, but in place of the fluorescent screen andwithin the envelope of the tube, a flat plate may be used as one of theanodes connected to one terminal of an output transformer, while anotherplate insulated from the first and mounted as closely as possible infront of the first mentioned anode has one of its edges shaped accordingto the contour of a composite sine wave constituting the algebraic. sumof a fundamentalwave and any number of harmonics thereof. This secondplate is connected to the other terminal of said transformer.

My invention will now be described in more detail, reference beingmade'to the accompanying drawings, in which Figure 1 showsdiagrammatically a preferred embodiment of the invention including acathode ray tube of the type hereinbefore mentioned and operatingcircuits therefor;

Fig. 2 shows a plan view of the anode plates against which the electronbeam is projected;

Fig. 3 shows a view similar to that of Fig. 2 but representing thecomposite wave formation for producing a tone of different quality fromthat which is produced by the wave formation of one of the plates ofFig.

Fig. 4 shows a modification of, the invention including a cathode raytube having a photoelectric screen and means for illuminating such I ascreen with a light and dark shaded pattern Fig. 8 is a representationof a characteristic image having a variable density pattern of light anddark areas, this image being suitable for pro- J'ection upon thephoto-electric mosaic screen of a cathode ray tube.

Referring to Fig. 1, I show a cathode ray tube having an envelope I, acathode 3, a focussing anode ii, deflecting plates 1 and 9, an anode Hpreferably of substantially rectangular formation, and another anodeplate l3 one edge of which has a contour of complex wave formation. Thecathode may be heated by any suitable source lb. The focussing anode 5is preferably of such formation as to focus the electron beam in anarrow web. As shown in the drawings, such a web would be verticallydisposed and would be projected between the deflecting plates 1 and 9. Asource of potential I! is connected between the cathode and thefocussing anode 5. Another source of direct current potential I9 isconnected between the lead to the focussing anode 5 and a mid-point onthe primary winding 2| of an output transformer 23. The two terminals ofthe winding 2| are connected respectively to the two anode plates II andl3.

In order to deflect the cathode ray beam laterally across the faces ofthe anode plates I l and I3, I may provide any suitable source ofalternating current such as the coil 25 within which a pure sine wavemay be generated by means of a tuning fork 21. The tuning fork may bekept in vibration by means of a driving coil 29 in circuit with a directcurrent source 3! and having an interrupter contact 33.

In .place of-the tuning fork generator I may, of course, employ aplurality of phonic wheels with pick-up coils mounted adjacent thereto.Such a construction usually has a phonic wheel disc for each note in themusical scale and these discs are mounted on a single shaft for rotationat a. constant speed.

-The control circuits to the deflecting plates 1 and 9 may include aresistor 35 bridged across the leads to the respective deflecting platesin order that a suitable load may be provided. The key 31 enable's oneto instantly start and stop the impress of deflecting impulses upon thedeflecting plates 1 and 9, even though the tuning fork 21 is-kept undera state of constant vi the composite wave produced by a clarinet. Otherwave formations may, of course, be utilized for simulating the differentorchestral instruments and various organ pipes having differentcharacteristic voicings.

Itwill be noted that in the illustrations of composite wave formationgiven in Figs. 2 and 3, the graph of a fundamental half wave extendsover the distance marked a. It is contemplated, therefore, that thedeflecting force applied to the plates 1 and 9 will be such as todeflect the electron beam back and forth over the entire areacomprehended by the dimension a and having a height b corresponding tothe vertical dimension of the webbed beam. Assuming, therefore, that thepure fundamental tone as produced by the tuning fork 2'! is allowed togenerate a deflecting force upon the plates 7 and 9, with the key 3!closed, then it will be seen that this fundamental wave will have suchamplitude as to cause the electron beam to scan the area ab.

When the tines of the tuning fork 21 are approaching the poles of thepick-up magnet 25 current will be generated in one direction of the coilthereof. This current will be reversed as the tines of the tuning fork21 move outwardly so as to increase the air gaps at the extremities ofthe core of the magnet 25. Accordingly, a full' cycle of the fundamentaltone frequency will result in the impress of charges on the deflectingplates I and 9 such as to move the electron beam forward and back overthe area (1b of the anode plates. It is for this reason that the contourc of the plate 13 is made to extend over only one half wave of thefundamental tone. The proportions of electrons simultaneously impingingupon the plates H and I3 will be equal at an intermediate point of thetraverse of the beam back and forth. At the extremities of thedeflection peaks of potential difference will be produced between thetwo anodes II and I3. The instantaneous values of the integratedharmonic forces will, therefore, be defined by the shape of the curveextending from one side to the other of the plate I3.

The periodic deflection of the electron beam causes the relativeproportions of electrons impinging upon the two plates ll and l3, tovary not only according to the fundamental tone of the tuning fork 21but also in accordance with thevarious harmonics of this tone which arealgebraically integrated for producing the complex wave 0 at the loweredge of the plate [3.

Referring now to Fig. 4 which illustrates a modification of myinvention. a. well known type of cathode ray tube 40 having a.photo-electric anode H is therein shown. This cathode ray tube isprovided with the usual electron emitting cathode 3, control electrode42, focussing anode 8 and accelerating anode 43. Deflecting coils and 45may be employed for causing the beam to describe a more or less circularpath as it impinges upon the photo-electric anode ll. In place of thedeflecting coils, however, electrostatic plates may be used, if desired.Such plates would ordinarily consist of two pairs, one pair being fordeflecting the beam according to a. vertical component and another pairaccording to the horizontal component of its deflection.

.The output circuit of an amplifier 38 includes the deflecting coils forthe vertical component. On the input side of amplifier 38 is a parallelcircuit arrangement of pick-up coils 4B3, 46, etc., these pick-up coilsbeing disposed suitably to be acted upon under the magnetic influence ofphonic wheels 13., "b, etc. As these phonic wheels rotate, electricwaves will be generated in motor.

2,241,027 the coils whose circuits are closed through the key switchesd8. Another amplifier 89 derives its control energy from the pick-upcoils 50a, 50b.

etc. when selected by the keys 68, and the amplifler output circuitincludes the cathode ray deflecting coils 45.

The phonic wheels 41 may be synchronously rotated in any suitable manneras by means of a motor '49. Each of the phonic wheels 41 has a peripheryof wavy formation, the number of scallops therein having a relation tothe speed of rotationsuch as to produce a desired fundamental tone ofthe musical scale. It has been shown in Patent #1,956,350 to Hammondthat a very close approximation to the equally tempered musical scalecan be had by using these phonic wheels as herein shown and by rotatingthe same under control of a single synchronous In order to providea'horizontal'component for the deflection of the cathode ray beam whichshall be displaced 90 in phase from the vertical component of thedesired fundamental wave, the deflecting coils 45 may be fed with energygenerated by any of the pick-up coils 50a, etc.. depending upon theparticular key switch 48 disposed with their axes relationship to thoseof the pick-up coils 46. That is to say, at any instant, the two pick-upcoils 46 and- 50 of a single pair are respectively opposed to points onthe wave pattern of the periphery of the rotor 41 corresponding to a 90phase displacement of Thus for each and every rotor 47 there will be a90 phase displacement between the energies generated in its cooperatingpick-up coils i6, 50.

With the;defiecting circuits provided as shown it will be understoodthat a cathode ray beam may be caused to describe an arcuate path aboutin a substantially 90 a circular area on the photo-electric anode 4|.

The anode ti may be ring-shaped, if desired, in order not to attractelectrons into the center zone. A single revolution of thebeam will becompleted within a single cycle of a fundamental note corresponding toone of the keys 48 when it is depressed.

The principles involved in supplying suitable potentials to thedeflecting circuits for a cathode ray tube for producing a rotarydeflection of the electron beam are well known in the art. Patent1,882,850 to Marrison is illustrative of the art. In that patent thecircular path. of the spot traced by the electron beam as it impingesupon the anode is explained on page 2, lines 31 to 34,, inclusive. 4

-1f,however, a chord is to be played by depressing several ofthe keys48, then the rotationone cycle of said pattern! v which is depressed;These pick-up coils 50 are the axis of the cathode ray tube. .Theangular velocity remains constant so long as a given algebraic summationof rotation velocity components of the different tones of a chordpersist. The wave motion, however, can be shown to be in exactcorrespondence with a resultant wave representing the instantaneous airpressures of the sound of a chord.

Now in order to give the fundamental tone as produced by the phonicwheel generator a desired timbre characteristic, I have shown means anda method for illuminating the photo-electric anode 4i with light anddark shaded patterns corresponding to complex sound waves, that is,sound waves made up of different harmonics of a. given fundamental tone,where each harmonic has a desired amplitude in relation to the others.

Suitably disposed in relation to the anode Al is an optical systemconsisting of a light source 5i, condensing lenses 52 and focussinglenses 53. Between the condensing lenses and the focusslng lenses I mayprovide a film or mask 54. Different portions of the film 54 may be usedfor casting silhouette pictures on the anode M. Silhouettesrepresentative of different tonal qualities may be obtained fromoscillographs of the sounds actually produced by different orchestralinstruments. I

An oscillogram of a single note will serve as a permanent record formodulating all of the notes .in the musical scale, according to themethods herein disclosed. Each silhouette picture when projected onto.the photo-electric anode M will .give a predetermined tonecharacteristic to the fundamental tones when played on the keyboard. Thesilhouette images shown in Figs. 5 and 6 are merely illustrative of manydifferent forms that may be used for simulating different instruments.

In place of the silhouette images as shown in Figs. 5 and 6, I may, ifdesired, produce equivalent results in modulating the fundamental tonesof the musical scale by varying the light intensity along differentradii from the center of rotation of the electron beam as it impingesupon the photo-electric anode 8|. Thus, one may elect to use variabledensity" sound films or variable translucent area sound films, as wellknown in the art.

It is well known that the anode M of a. cathode ray tube such as hereinshown may be arranged to respond to different degrees-of illumination,thereby to generate a current of. variable amvelocity as produced by thedeflecting coils M and 45 will vary according to the resultant of thevarious electrical forces generated by different onesof the pick-upcoils 46 and 50. Such a condition corresponds with variations in theinstantaneous air pressure at a given point. in a room where sound wavesare being propagated. It is, therefore, evident that on thephoto-electric screen of a cathode ray tube I may cause an electron beamto traverse different portions with different velocities. so as tosimulate the resultant of as many of the fundamental tones as it isdesired to sound simultaneously, the same as in playing chords on of thekeyboard type.

These different velocities are obtained by varying the radius of thebeam in its deflection from any musical instrument an output circuit isherein shown as including a source of potential 55 for obtaining thedesired polarity on the anode 4i more positive than on the acceleratinganode 33. In circuit between the 'source 55 and the cathode 3 is aprimary winding of a suitable transformer 56. The secondary winding ofthis transformer may be fed to an amplifier-57 and thence to a loudspeaker 58. The anode-to-cathode circuit may also include an additionalsource of potential 59 for producing a voltage on the acceleratingelectrode 43 more positive. than that of the cathode 3. r

A biasing source M is connected between the,

varying the potential on the focussing anode 8 in order to control thediameter of the spot where the beam impinges upon the anode 4I-.

In the operation of my invention as illustrated in Fig. '4, it will benoted that various modulations ofthe fundamental waves may be derivedfrom the cathode raytube according to the particular wave pattern whichis projected as a picture on the photo-sensitive anode 4|. Variations inthe wave pattern may well be provided on a single film 54 or onaplurality of such films selectively introduced into the path of thelight beam from the lamp 5I., Furthermore, it may be seen that differentfilms and different sources of light may be-arranged so as to throwdifl'erent images selectively upon the photo-electric anode Merely forthe purpose of illustration, and for the sake of simplicity of showingmeans to an end, I have indicated the use of a control knob 93 onthesame shaft with a gear 'M meshed with another gear 75 on the shaft ofoneof the reels 68 whereby the film 54 may be wound or unwound in orderto bring difierent sound pictures into the path of the'light beam.Tension may behad on the film 54 for rewinding purposes by the aid of acoiled spring 61 connected with the winding spool 68. A suitableindicator scale 59 may be disposed for cooperation with a pointerwhereby the turning of the control knob 63 will indicate what particularsound record and hence 'what particular tone quality is to be had byStill another modification of my invention conand thus to impinge uponthe front and back anodes I3 and II respectively in varyi ng proporons.

In order to provide an organist with means for playing a melody passagehaving one tonal charact'eristic, simultaneously with anaccompanimenthaving a diflerent tonal characteristic or I combination ofcharacteristics, it is within the scope of my invention to utilize aplurality of manuals together with a pedal keyboard. It is, therefore,contemplated that each manual will beconnected through difierentconductors 84 to appropriate deflecting circuits for respectivelydiflerent cathode ray tubes. Each cathode ray tube will then have itsown optical system and set of sound record films corresponding to the"stops that are to be selected for a given manual. A duplication ofapparatus as thus suggested'will also be found useful in combinationwith a pedal keyboard. Furthermore, each cathode ray tube, as controlledby a separate keyboard,.inay be provided with an independentoutput/circuit and amplifier, the amplifier havingits own volume controldevice 85, whereby the relative intensities of volume of a, solo passageand its accompaniment may be regulated at the discretion of theorganist.

Referring now to Fig. 7, I show another modification of my inventionwhich is particularly adapted to an electronic musical instrument havingtwo or more manuals and a pedal keyboard. The figure shows in elevationkeys I0 and 11 of two different manual keyboards and keys 78 of a pedalkeyboard. Each of'these keys, both of the manual and pedal keyboards, isprovided with a contact plate l9 which, when a. key is depressed, putsground potential on an appropriate key circuit 90 leading to a givenfundamental frequency oscillator 8|, 82 or 93.

- The oscillators BI, 82 and 83 may be of any desired type. For example,they may be tuning forks like the fork 2? shown in Fig. 1, or they maybe rotating discs like the discs 41 in Fig. 4, or again they may be inthe form of electron discharge tubes having tuned circuits formaintaining a given pitch corresponding to the note of each appropriatemanual or pedal key.

All of the oscillators for the full range of notes in the upper manualkeyboard are connected in parallel to an output circuit conductor 84leading to the screen grid 85 in a control tube 86. This tube preferablyis of the pentode type and is normally biased to cut-off by a suitablesource 89, connected in circuit between the cathode 88 and a biasresistor 90 leading to the control grid 81.

The output circuits of the oscillators 82 (appropriate to the lowermanual) are similarly connected in parallel to a conductor 9I leading tothe screen grid 92 of a control tube 93. This tube and the tube 94 arethe equivalents of the tube 86. Tube 94, however, is provided with ascreen grid 95 which is connected by conductor 96 to the respectiveoutput circuits of the oscillators 03 for the pedal keyboard.

The tubes 86, 93 and 94 are used to impress modulations upon the outputof a supersonic frequency oscillator 91 which delivers preferably a sinewave of, for example, 71 kilocycles to a frequency modulator 98.Frequency modulators are well known in the art and need nofurtherdescription in this application.

In order that the efiectsof playing a musical piece on'difierent manualsand the pedal keyboard may be additive with respect to the portionsplayed on difl'erent keyboards, I provide means for allotting smallmutually exclusive intervals of time to each keyboard successively. Therate of shift of control from one manual to the other, and to the pedalkeyboard, must, of course, be at a supersonic frequency. Accordingly, Ipreferably provide a saw-tooth wave oscillator 99 for controlling acathode ray tube I00 having a plurality of anode targets IOI eachcoupled by means of a capacitor I02 to the cathode of a. respective tube86, 93 or 94. The cathode ray tube is provided with beam deflectingmeans such as the deflector plates I03, each connected to its respectiveoutput lead from the oscillator 99. The cathode ray tube I00 is provldedwith the usual electrodes constituting an electron gun. Suitablepotentials for these electrodes are obtained from the direct currentsources I04, I05 and I06. The source I04 biases the control gridnegatively with respect to the cathode, the bias being made adjustableby means of a variable resistor I01. A positive potential from sourceI05 1 impressedupon a focussing anode and also upon oneof the deflectingplates I03. The opposed deflector .plate I03 is also maintained at thispotential plus or minus the output potential from the oscillator 99. Thesource I06 renders the targets IOI positive with respect to all otherelectrodes of the electron un. As the electrons impinge upon eachtarget, the positive potential thereon is reduced, thus putting anegative charge on the associated ca- 2,241,027 pacitor I92 which iscoupled to the cathode of one of the tubes 89, 99 and 99. These tubes,therefore, become conductive one at a time and in rapid succession, sayfor periods of second.

While each key depression causes an appropriate tone frequency to beimpressed upon the screen grid in one of the tubes 89, 93 and 94, theconductive time intervals of each tube recur with such rapidity as toform well defined envelopes of the tone frequency waves from theoscillators 8|, 82 and 83. When solo passages are played on one keyboardthese envelopes have a sine wave characteristic and a frequencycorresponding to the fundamental tone of each key. When chords areplayed, the tone frequency envelopes become complex just like the soundwaves which are propagated in air. The composite action resulting fromplaying the keys of one or more keyboards simultaneously will,therefore, be to impress'these difierent frequencies from theoscillators 8|, 82 and 83 selectively upon the frequency modulator 99,the output from which develops frequency modulated supersonic wavesacross the primary of a transformer I 08.

It is perfectly feasible, in accordance with the embodiment of myinvention shown in Fig. 7, to simultaneously apply the tone frequenciesof different keys to the control tubes, and thence to the frequencymodulator 98, as when playing chords. What happens in this case is thatthe frequency of the oscillator 91 is modulated over any part of theaudible frequency band from the lowest to the highest notes in thekeyboards.

In order to provide variations in the dynamic relationship between thenotes played on the upper and lower manuals, I may, if desired, em-

ploy a potentiometer I09 having a movable tap IIII for feeding outputpotentials from the tubes 96 and 93 to' the modulator 98; It will beunderstood that these output potentials are determined by theconductivity of the discharge tubes 86 and 93, and by the direct currentpotential from the source I feeding through the control circuit for themodulator 99. 7

If it is desired that the notes played on the two manuals shall have thesame modulation depth, then the potentiometer tap IIII may be speakerI51. Each of these tilting pedals I53,

I56 and I55, may, if desired, be connected to its appropriatepotentiometer by either electrical or mechanical means. For the sake ofsimplicity and 94 are a composite of the potentials derived from theoscillators BI, 92 and 93 and the superplaced mid-way between theterminals of the potentiometer resistance I09. In this position impulsesof equal amplitude will be derived from the two tubes 99 and 93 to beimpressed upon the frequency modulator '98. If, however, it is desiredthat the notes of the upper manual I6 be emphasized over those of thelower manual 11-, then, by operation of a gtilting pedal I53, thepotentiometer tap IIII may be moved to the left, thus reducing theimpedance offered to the currents passed through the tube 88 whileincreasing that impedance which is offered to the-current passed throughthe tube 93. The reverse action may, of course, be obtained by tiltingthe pedal I53 in the other direction.

The dynamic effects of the pedal keyboard oscillators 83 may likewise becontrolled independently of the other oscillators by employing stillanother tilting pedal I54 to control a potentiometer H5 in circuitbetween the anode of the tube 94 and the common modulator circuitleading through the unit 98. A volume control device for the entireoutput from the musical instrument may be in the form of still anothertilting pedal I55 connected to a potentiometer IIG for controlling theaudio output from amplifier III. The energy from this amplifier is fedto-a loud posed potential from the source II2, the positive end of whichis grounded and the negative end of which is connected throughresistors.ll3 to the respective cathodes of these tubes. The keys I6, IIand I8, as has been stated, operate to complete different circuitsselectively which may now be traced from ground, through an appropriateoscillator such as 8| and common conductor 84 to the screen grid 85,thence through the discharge path of the tube 86 to its cathode, throughthe resistor II3 to the negative end of the source II2, the positive endof this source being grounded.

From the above description it will be seen that output currents from thetubes 89, 93 and 94 will be derived from'gthe anodes of these tubes andwill be fed to the frequency modulator 99, anode potential beingsupplied by the source I in series with the source II2. These modulatingpotentials will possess all of the characteristics of the fundamentaltones appropriate to the depressed keys, whether they be played inchords or. in solo. quency modulator 98, when impressed upon thetransformer I99, operates to control the deflection of an electron beamin the cathode ray tube I20.-

This tube is preferably of the type known as an iconoscope andpossesses, in addition to the usual electrodes of an electron gun,horizontal deflecting plates I2I and vertical deflecting plates I22. Thetube I29 also possesses a photoelectric screen I23 having a. conductivefilm in back thereof which is connected inan output circuit I24 leadingthrough a load resistor I25 to ground. -This tube also possessescollector electrodes I26 and I21, which may be in the form of metallicdeposits on the inside walls of the tube and which may, if desired, becarried at different potentials, although, for the sake of simplicity, Ihave shown them both connected to ground. The focussing electrode of theelectron gun is indicated at I28 and this also is grounded. A negativepotential with respect to the focussing anode I28 is derived from thesources I29 and I39 for impress upon the cathode I3I' of the. electrongun. A suitable negative bias may be obtained from the source I32 forimpress, across a resistor I33, upon a control grid I34. The mosaicscreen I23 is arranged to receive a light image from an optical systemconsisting of a source of light I35 and lens systems I35 and I31.Between these lens systems and at the focus thereof 1' preferablyinterpose any one of a multion a predetermined family of harmonicssuitable for simulating the timbre quality of any desire musicalinstrument.

- In order to vary the timbre of the tones played on the manuals and thepedals, I may employ The output energy from the freany selected one of anumber of these films as shown in a magazine 638. The films Q39 areindicated in cross section andeach may be pushed into operative positionin the optical system. One of these films is shown at I390. held inplace by a gateway of the magazin I38, this gateway having an openingfor admitting light from the source I35. The light beam, after it 7traverses the film and the lens arrangement I3l,

will focus an image upon the mosaic screen 523 in accordance with thelight and dark areas of the selected film. Each film selection may beobtained by means of a suitable stop I40 which is conveniently disposedto be pulled out at will by the organ player When a stop is pulled outit operates some suitable mechanical or electrical control system forlowering a selected film into the film gate, so that the image of thefilm may be used to modulate the fundamental waves which are impressedupon the deflecting plates IN and I22 within the cathode ray tube I 20.

It will be noted that the rotation frequency applied to the deflectingplates I26 and i 22 is varied between two supersonic limits, one ofwhich may, for example, be considered as 71 kilocycles, and the other ofwhich may be the same number of cycles plus the highest frequency of anyof the oscillators M, 82 and 83.

The rotative action upon the electron beam in the iconoscope tube 1120may be produced by any suitable phase splitting device such as willimpress on the horizontal deflecting plates I2I a potential having asubstantially 90 phase relation to the potential which is applied to thevertical deflecting plates I22. For the sake of simplicity, such a phasesplitting device is represented as a combination of a resistor Mi and acapacitor I42. The impedances of these two elements should be equalizedat the mean frequency, that is, at th frequency of the oscillator 91plus the frequency of the middle note in the keyboard. It is true thatthis arrangement will for higher and lower notes of the keyboard producedepartures from the 90 phase relationship which is desired for rotativescanning. However, the

frequency of the oscillator 97! is made sufilciently high so that thesedepartures over the audible range will be slight and not undesirable. Infact; such departures as may occur unavoidably will tend to deflect theelectron beam in an elliptical path so as to produce a vibrato effect inthe output energy, and thus to simulate the sound of a stringedinstrument which is played in a vibrato manner. If, however, theparticular arrangement of resistor MI and capacitor I42 is foundinadequate to meet the phase splitting requirements, then other phasedisplacing apparatus well known in the art may be employed.-

Since it is desirable that all of the minute variations in the curvatureof the image derived from the characteristic film may be scanned by theelectron beam, it is one of the features ofmy invention that thedeflecting forces shall include a very rapid radial component. radialdeflection may be obtained from an oscillator I43 which deliverspreferably a sine wave of the order of 3 megacycles. Several diflerentmethods of radial beam deflection are available. The method shown in thefigure is one in which I employ a conical shaped electrode I whose axisis coincident with the central axis of the electron gun. This electrodeis connected to one terminal of the output circuit of an oscillator I43,the other terminal of this oscillator being preferably connected to thejunction between the sources tit and 83B. The relative potentials of thesources 829 and we are such that a suitable bias may be impressed uponthe electrode M8 for producing a centrifugal deflection of the electronbeam. This defiection will vary in extent in accordance with theoscillation energy which is delivered by the oscillator I43. The actionwill be so rapid, however, that a great many radial movements will begiven to the electron beam while it circumscribes only once thering-shaped pattern of light and dark areas on the mosaic screen 923.

If it is not desired to employ such an electrode may be unnecessary toemploy the very high frequency oscillator I43, since even an ellipticalpath which the beam may circumscribe will not cause any appreciabledistortion of the harmonic components which are to be impressed upon thefundamental frequencies.

It will be noted that the sum-frequencies representing different audiowaves impressed upon the supersonic frequency output from the oscillator@i will be still further modulatedby the characteristic wave shapingaction produced by one of the films I39, when the image thereof isprojected on the iconoscope screen I23. It is necessary, however, toprovide a stroboscopic effeet in order to apply these timbrecharacteristics to the audio frequencies alone. This is accomplished,according to the invention, by varying the density of the electronbundle in the cathode ray under control of the high frequency from theoscillator 31. Accordingly, I employ a capacitor M3 to take off acomponent of the high frequency from the oscillator 9i andto impress itupon the control grid I34. This causes the number of electrons in theelectron stream to vary at the same rate as the cyclic rotationfrequency applied to the deflecting plates Hi and I22 when no audiblefrequencies are imposed upon the modulator 98. In the absence offundamental audio frequency modulation, therefore. the mosaic screen I23will be rotationally scanned at the same frequency by which the electronstream is varied in intensity. When, however, modulations are appliedthrough the unit 38, the position of maximum emission from the electrongun will rotate about the periphery of the screen I23 at variablevelocities dependent upon the fundamental Such a Q tone frequencieswhich are derived from the oscillators 8|, 82 and 83.

Although the amplitude bi the carrier wave delivered by the oscillator91 is constant, the amplitudes of the audio waves as delivered by therespective tubes 83, 83 and 84 may be varied by means of the volumecontrol pedals I33 and IE4 so as to vary the modulation depth, and henceto vary the dynamic content of the output from the modulator 93. Theresult of this volume control action is to vary the mean radius ofcurvature of the path described by the beam-spot" on the mosaic screenI23. This 2,241,027 is true for the reason that the deflecting potentials applied to the plates I2I and I22 will be dynamically varied. Inorder, therefore, to give effect to these dynamic variations and todifferentiate between the energies representing tones played ondifierent manuals, and on the pedal keyboard, it is desirable that therange of shading of the light and dark areas imaged upon the screen I23should be graduated between the outer and inner margins of the ring.Where the ring area is illuminated around substantially the entire outerperiphery as in Fig. 5, and is darkened around substantially the entireinner margin, this effect may be produced automatically. This is truedespite the action of the oscillator I43 to swing the electron beam inaccordance with a radial component. If the resultant deflection tends toseek the inner margin of the ring, then thescanning action will cover apredominantly dark area. On the other hand, with higher amplitudes andgreater deflection, the light areas on the outer margin of the ring willbe predominantly scanned. In order to provide suitable regulation of thedynamic effect of the radial deflection from the oscillator I43 apotentiometer I41 may be employed.

When the image projected uponthe screen I23 is of thevariabledensitytype as shown in Fig. 8, this image should preferably be formedso as to provide maximum contrast of shading, say, on

the outer margin of the ring and minimum con-p trast of shading aroundthe inner margin thereof. The arcuate variation of shading representsthe composite characteristic of the various harmonic frequencies whichare to be applied to give each fundamental' frequency its desiredtimbre. The amplitude variations which are to be' derived from thescanning action will, how-' ever, be determined by the extent of thedeflection due to the deflecting plates I2I and I22, so

that smaller amplitudes will be developed in the output from the cathoderay tube when the beam'seeks the inner margin of the scanning ring andlarger amplitudes when it seeks the outer margin thereof.

, The output energy from the tube I20 is impressed across a loadresistor I25 so as to produce voltage variations therein. These voltagevariations are also impressed upon a capacitor I58 for the purpose ofactuating .suitable deas when heterodyning is used. The apparatus willalso include suitable filtering means for eliminating undesirablefrequency components. Furthermore, the apparatus will require sufllcientamplification means to produce usable audio waves in a loud speaker I51.

In operation'the signal derived from the conductive film on the back ofthe mosaic screen I23 may be accounted for as follows:

Consider first, the action of the tube when the mosaic is scanned by thebeam with no illumination on the mosaic. When the electron beam strikesa globule, the globule emits secondary electrons, the number ofsecondaries being'several times larger than the number of beam electronsstriking the globule. Some of these secondaries return almostimmediately to the globule, the

rest escape and go either to the collector or to other parts of themosaic. Because the globule is insulated, its potential will change inthe positive direction if the number of electrons escaping from it isgreater than the number of electrons flowing to it. The number ofelectrons which escape dependson the potential of the globule, thenumber being less, of course, the

more positive the globule is. Hence, if the beam is on the globule asuiflciently long time, the globule will be driven to a positivepotential. The value of this potential for typical operating conditionsis about 3 volts positive with respect to the collector.

After the beam passes the globule, some of the secondary electronsemitted from the rest of the mosaic fall on the globule. The arrival ofthese electrons changes the globule potential in the negative directionto anew value. In a typical operating condition, this value is about 1/2 volts negative with respect to the collector. With no light on theglobule, the globule stays at this negative potential until the nexttime the beam strikes, when the globule again releases electrons andrises to its maximum positive potential of approximately 3 volts.

Consider now the action of the tube when the mosaic is scanned with partof it illuminated. During the time between contacts with'the beam, bothan illuminated globule and an unilluminated one receive electrons fromthe rest of the mosaic. Both globules, therefore, charge in the negativedirection during this time. The illuminated globule, however, at thesame time emits electrons, the emission being caused by the light onthis globule. The illuminated globule, therefore, does not fall to asnegative a potential as the unilluminated one does. Hence, the next timethe beam strikes, the illuminated globule does not have as far to riseto reach 3 volts? As a result, less charge is Ereleasedto the collectorwhen the beam strikes the illuminated globule than when the beam strikesthe unilluminated one.

As the "spot moves over the mosaic, varying amounts of charge flow fromthe individual elements of the mosaic to the collectors I26 and I21. Theamount of charge flowing at any instant is a measure of the light on theglobules where the beam is at that instant. In other words, a signalcurrent flows between the mosaic and the collector. Although the beamcurrent in an ordinary iconoscope tube is constant, in this case it isvaried by the control action upon the electrode I34. The resultantsignal current across the resistor I25 is, therefore, a composite of thecontrol action by the control electrode IM and of the photo-electricresponse to the light energy derived from the image impressed upon themosaic screen I23. The voltage developed across the load resistor I25will vary in accordance with the audio frequencies impressed upon thefrequency vmodulator 98, since the respective components of theoscillator 91 impressed upon the control grid I36 and upon thetransformer I08 are such that no variation in the signal output wouldresult except for the photo-electric action of the image on the screenI23. The stroboscopic efiect' is such as to vary the angular velocity ofthe beam scanning action, while the frequency applied to the controlgrid I34 remains constant.- This enables me to derive suitabletimbre-characterized audio frequencies from the output circuit of thetube I20. v

It is apparent that numerous advantages may be obtained by carrying outmy invention in the manner hereinbefore set forth. The timbrecharacteristics of any number of solo instruments, as well as anyorchestral group of instruments, may be transcribed from actualrenditions on these instruments. The permanent records thus obtained areusable at will in an instrument of relatively low cost and one whichoccupies a space not appreciably greater than an ordinary organ console.The exact simulation of tone qualities of notes produced by costlyinstruments and by differently voiced organ pipes is made possible. Theflexibility of control by shifting alternative records into serviceprovides the utmost of convenience to an organist and a very I greatrange of possibilities for artistic interpretation of a musicalcomposition.

Various modifications of the invention other than those herein shown anddescribed may suggest themselves to those skilled in the art.Accordingly the invention is limited only in accordance with the scopeof the claims.

I claim:

1. A musical instrument having keys to be played, a. tuned audiofrequency oscillator under control of each key, a cathode ray tubecomprising an electron gun, beam deflecting means, and a photo-electricscreen; means for projecting on said screen an image graphicallydepicting the timbre characteristics of a tone to be reproduced, saidimage constituting light and dark portions of an annular area, means forimpressing supersonic frequency potentials upon said deilecting meansthereby to scan said annular area rotatively, and means for causing saidpotentials to be frequency-modulated by output energy. from thekey-actuated audio frequency oscillators.

2. A musical instrument according to claim 1 and having detector andamplifier means re- I ceptive of output energy from said cathode raytube, and a loud speaker controlled by the last said means.

3. A musical instrument according to claim 1 and having a beam-intensitycontrol circuit connected between the cathode and control grid of saidcathode ray tube, and means including a supersonic frequency generatorcoupled to said control circuit for varying the electronic density ofthe cathode ray ata predetermined periodicity.

4. A musical instrument according to claim 1 and having means forinjecting. alternate centrifugal and centripetal components into thescanning of said screen by the said beam, said components alternatingat'a frequency considerably higher than that of said supersonicfrequency potentials.

5. A musical instrument according to claim 1 and having said keysgrouped in different keyboards, and means for causing the modulationsimpressed on said supersonic frequency potentials to be constituted byan integration of brief impulses occupying mutually-exclusive timeintervals, successive impulses being derived from different oscillatorsappropriate to respectively difierent keyboards.

6. A musical instrument having at least one keyboard and a plurality ofelectric tone freing a heterodyned audio frequency derivativequencygenerators each under control of a difnism with the frequency-modulatedcycles from said source, a photo-electric mosaic screen in said tubehaving an annular area on which to trace the path of the scanning spot,luminous projection means adapted to focus. an image .on said mosaicscreen, said image being so characterized as to produce variations inthe output energy from said tube when scanned by said spot, means fordemodulating said output energy thereby to derive electric audio waveshaving the same fundamental frequency components as those of the outputenergy from the key-actuated tone frequency generators and havingsuperimposed harmonic components of which said image is a. graphicrepresentation of one fundamental frequency cycle, and means fortranslating said electric audio waves into corresponding sound waveshaving a desired timbre characteristic.

7. A musical instrument according to claim 6 and having a plurality offilms cooperatively associated with said luminous projection means, eachfilm bearing an appropriate circular image to be projected upon saidmosaic screen, and a plurality of selectively operable stops arranged tobe manipulated by an organist, each stop having means connected theretofor interjecting one of said films into the luminous path of said pro-Jection means.

8. A musical instrument having electric switches each operable by anappropriate key of a keyboard, sources of electric wave energy ofmusical scale frequencies, each source being operable to deliver itsoutput in response to the actuation of an appropriate one of saidswitches by its respective key, a cathode ray tube having rotativedeflecting means, a supersonic frequency source connected to saiddeflecting means and operative to rotate the beam cyclically, means forfrequency-modulating the energy from the last said source by 'energyfrom the first said sources, means interposed between the modulatingmeans and the deflecting means for phasesplitting the modulated energy,means including a target electrode in said cathode ray tube operativewhen scanned by the beam spot to produce a wave-shaping action upon eachcycle of output energy from said cathode ray tube, means forheterodyning the frequency-modulated and wave-shaped energy with a fixedsupersonic frequency, means for detecting and amplifying the heterodynedenergy, and a sound reproducing device under control of the last saidmeans.

9. In a musical instrument, means for producing an electron stream,deflector means for imparting rotary movement of said stream in cyclesof a supersonic frequency, means capable of producing oscillations atdifferent musical scale frequencies, means for frequency modulating thesupersonic cycles by said oscillations, a waveshaping element adapted tobe variably excited when scanned by said stream, means for obtainfromthe cooperation of said wave-shaping element with the scanning thereof,and means controlled by the last said means for producing musicalsounds.

10. The device according to claim 9 in which said wave-shaping elementis constituted by a photo-electric mosaic screen in combination with anoptical system comprising means for projecting a. characteristicwave-shaping image thereon. I

-11. In a device for introducing timbre-characteristics into fundamentalfrequency tones, means for producing oscillations representing saidtones,

means for producing a directed beam of electrons, a target for saidbeam, means for causing said target to be rotatably scanned in cycles ofa supersonic frequency, means for causing the instantaneous velocity ofsaid cycles to be modulated by selected single trains of said tonaloscillations and by concurrent combinations of said trains, means formodulating theelectronic density of said beam at a fixed supersonicfrequency, means rendering said target operative when scanned by thebeam to effect amplitude modulation of an output current derivative ofthe scanning action, and means to utilize said output current derivativefor the production of timbrecharacterized musical tones.

e 12. In a musical instrument, a cathode ray tube having aphoto-electric target electrode, means for contrastingly illuminatingdifierent areas of said electrode, the margin line separating light anddark areas being endlessly conformed to the vector graph of a complexsound wave, means for causing the electron beam in said tube torotatively s'can said light and dark areas at difierent velocities independence upon the frequencies of selected musical scale notes to beplayed, an

output circuit for said tube, and means controlled by said outputcircuit for reproducing a train of sound waves corresponding to saidmusical scale notes when modulated by said complex wave;

13. A device in accordance with claim 12 and including means forsuperposing a supersonic frequency radial deflection component on thscanning action of said electron beam.

14. In a musical instrument, an electron dispredetermined timbrecharacteristic, the last said means being controlled by said outputenergy.

15. A device in accordance with claim 14 in which said means forcontrolling the scanning velocity includes a supersonic frequencyoscillator, a quadrature phase-splitting device interposed in circuitbetween said oscillator and said beam deflecting means, and means forfrequency modulating the output energy from saidoscillator.

16. A musical instrument of the class described comprising a cathode raytube having an electron gun, a target, and electron beam deflectingmeans; means for so characterizing said target that, when rotativelyscanned at cyclic frequencies which are a function of selectedfundamental frequencies representing musical notes, potentials areproduced having a desired timbre eifect, means for applying operatingpotentials to said beam deflecting means, and means controlled by outputenergy from said tube for reproducing said musical notes embellished bysaid timbre efiect.

17. A musical instrument having a plurality of manual keyboards and apedal keyboard, means for producing fundamental frequencies inrosponseto the playing of the keys of said keyboards, means for separatelycontrolling the relative amplitudesot the frequency products appropriateto each keyboard, sound producing apparatus comprising an electronicdevice for superposing complex harmonic frequency components upon saidfundamental frequencies, and means including an electronic distributoroperative at a supersonic switching frequency for applying saidfundamental frequencies appropriate to the played keys of each separatekeyboard in succession during mutually exclusive time intervals.

18. A musical instrument having a plurality of keyboards, a fundamentalfrequency electric generator for each key of the musical scale in eachkeyboard, cyclically operable switching means for rendering thegenerators of different keyboards efiective in mutually exclusivetimeintervals, an oscillator for controlling the cycles of said switchingmeans at a supersonic rate, a volume control device for varying theenergies delivered by said generators in accordance with the relativeamplitudes to be derived from playing the keys of different keyboards,an element carrying a-graphic' representation of a single cycle of asound wave having harmonics thereof superimposed, thereby to simulate atone of given timbre, means under control of said record for causing theoutput energy from said generators to be modulated in accordance withthewave formation of said graphic representation, and means fortranslating the modulated energy into musical sound waves.

19. In an electronic musical instrument, means for producing electricwaves of different audio frequencies corresponding to the fundamentaltones of a musical scale, a cathode ray tube having electron emittingand beam iocussing means and a target electrode to be scanned by anelectronic spot, said target electrode constituting means forsuperimposing harmonic frequency modulations upon the output energy fromsaid tube which modulations are correlated with selected fundamentalfrequencies of the first mentinned waves, means providing a complexscanning path for said spot such that one component is oscillatory at asupersonic frequency in a.

radial direction while another component is rotative at a cyclicfrequency dependent upon selected waves derived from the first saidmeans, and means under control of output energy from said cathode raytube for producing complex tones which are characterized by saidfundamental frequencies and by said harmonic frequency modulations.

RALPH w. BUMS'I'EAD.

